From open landscapes to forest refugia: Human encroachment and climate change as drivers of red deer (Cervus elaphus) niche shifts over 21,000 years

The red deer (Cervus elaphus) is one of the few remnant species of the European Pleistocene megafauna. It occupies a wide range of habitats across the Holarctic, yet the factors shaping the species’ realized ecological niche over time remain poorly understood. To investigate these dynamics, we analysed published stable carbon and nitrogen isotope data from 623 bone collagen samples spanning 21,000 years in Europe. The δ¹³C values, considered as a proxy for feeding habitat, demonstrate that red deer foraged in open landscapes during the Late Pleistocene, whereas in the Holocene they primarily inhabited forested environments. Although δ¹⁵N was expected to reflect dietary changes associated with this habitat shift, our analysis reveals that its variability was more strongly associated with climatic fluctuations. Notably, the species’ isotopic niche expanded from the Late Pleistocene to the Holocene but has since contracted toward the present. To assess the factors shaping these niche dynamics, we modelled the influence of mean annual temperature, precipitation, human population density, and elevation. Our results demonstrate that temperature, precipitation, and human activity best explain isotopic variability. Yet, while environmental changes conditioned niche dynamics in the Late Pleistocene and Early Holocene, the marked human demographic expansion of the Middle Holocene led to anthropogenic pressures becoming the dominant driver. Against this backdrop, we propose potential future scenarios for this species, considering its ecological plasticity, human encroachment, and the implications of ongoing environmental change for conservation and rewilding.